The present invention relates to shock absorbers such as hydraulic shock absorbers that generate a damping force by controlling the flow of a hydraulic fluid in relation to the stroke of a piston rod.
Hydraulic shock absorbers attached to the suspension systems of vehicles, for example, are desired to have optimal damping force characteristics in order to improve ride quality and steering stability. In general, this type of hydraulic shock absorber has a piston connected to a piston rod and slidably fitted in a cylinder having a hydraulic fluid therein. A stroke of the piston rod causes sliding movement of the piston in the cylinder, which in turn induces a flow of hydraulic fluid. The hydraulic fluid flow is controlled by a damping force generating mechanism, which comprises an orifice, a disk valve, etc., to generate a damping force, and the damping force characteristics are adjusted on the basis of the flow path area of the orifice, the valve opening characteristics of the disk valve, and so forth.
A hydraulic shock absorber disclosed in Japanese Patent Publication No. 2006-10069 has a back pressure chamber and a main valve at the back of the disk valve of the damping force generating mechanism. The main valve relieves the pressure in the back pressure chamber to the downstream side. A part of the hydraulic fluid is introduced into the back pressure chamber, and the pressure in the back pressure chamber is applied to the disk valve in the direction for closing the disk valve, thereby adjusting the valve opening pressure of the disk valve, and thus increasing the degree of freedom for setting damping force characteristics.